The present invention relates to cameras.
In particular, the present invention relates to cameras which are capable of automatically determining exposure time by way of a digital structure which cooperates with the shutter to determine the exposure time in accordance with factors such as the light intensity.
The invention is particularly applicable to cameras having through-the-lens light-measuring systems and wherein the exposure time is capable of being set in a stepwise manner according to discrete quantities.
While exposure-time determination of this latter type is highly desirable in certain respects, it has the disadvantage of presenting certain inaccuracies where the actual light intensity does not coincide with one of the discrete quantities used for determining the exposure time. Thus, with an analog type of electric shutter where the exposure time is determined with a timing capacitor which memorizes the light intensity as a voltage value, the exposure time is determined in a non-stepwise manner. However, where the quantity corresponding to the light intensity is memorized in a digital form, the light intensity which actually is a continuously varying quantity, is capable of being memorized only as an approximate discrete quantity, so that it is not possible with such a construction to obtain a non-stepwise determination of the exposure time.
With a so-called digital type of exposure time determination where the photographing light intensity is converted into a number of pulses which is memorized by a counter circuit and the shutter time is controlled in accordance with this memorized value, if it is desired to increase the accuracy of the exposure time, it is essential to utilize a relatively high frequency of pulse oscillation and to increase the number of memory stages. However, with constructions of this latter type where discrete, quantized digital values corresponding to light intensity are memorized, it is inevitable that there will be a certain quantization error, and thus this latter unavoidable error when using digital types of memory devices will unavoidably introduce undesirable inaccuracies in the exposure time.